No set ways for me. I still horde VHS movies because they are dirt cheap and I buy a lot of comedies and the benefits of DVD just don't do that much for that type of movie.
For rentals, I nab the 3 VHS for 3 nights for $3.00. On the nights when I can get two DVD's for $3.50 I'll go that route.
As for purchases, I hit blockbuster up for their $7.99 used DVD deals or their $3.99 used VHS tapes. Best Buy has also been offering pretty decent DVD deals as of late.